1. Field of the Invention
The present invention relates to metrication of machine torque characteristics and the electronic integration thereof, and more particularly for determination of work input to production machinery, especially in the plastics compounding and food mixing processes.
2. Description of the Prior Art
In the past, work expended in mixing has been measured by integration with respect to time of the electrical power utilized in operating production machinery and thereby derive an estimate of shaft horsepower. Typical of this approach is the U.S. Pat. 3,951,389, issued Apr. 20, 1976 to John P. Porter and entitled, "Elastomer Processing Method." The Porter patent teaches monitoring electrical power consumed by an elastomer processing apparatus under load conditions, compensating the quantum obtained by reducing the same by the amount under no-load conditions to arrive at a net power consumed for process work, converting the net power consumed to an electrical signal, and then integrating the signal with respect to time to provide an output for control purposes. However, a device for determining the integral of mixer to torque with respect to time is not within the teaching of Porter. At present laboratory models of torque rheometers are used throughout the polymer processing industry as quality control and research instruments. Torque rheometers provide a continuous readout and/or recording of torque during mixing and can be equipped with various high shear mixing heads or extruders to simulate specific production processes. The torque rheometer provides the formulator, processor and end user with the means to derive information needed to assure processing uniformity from batch to batch and guard against reject and waste. In the case of plastics and elastomers, for example, it is vital to understand how a given formulation reacts to specific production equipment and processing conditions. The torque temperature data obtained from laboratory torque rheometers is related to polymer processing characteristics and can be used only as a relative measure. Torque temperature data alone does not provide a measure of work input. Work input measurements have been shown to provide an accurate means of controlling processes to reach optimum properties. For example, overmixing polymeric compounds can result in polymer degradation and wasted energy; and undermixing can result in improper dispersion causing poor physical properties.
Recently much research has been done in the area of predicting general processing characteristics polyvinyl chloride (PVC) such as dynamic thermal stability, melt flow properties, and fusion and melting aspects of PVC compounds. Recent studies such as that of Pravin L. Shah entitled "Predicting PVC Extrudability from Melt Temperatures," SPE Journal, Vol. 29, No. 4, April 1973, have been published. Shah found that the Brabender Plastograph can be used to predict extrudability of PVC compounds. Significantly, from a practical standpoint, the method did not require conversion of Brabender data into formal rheological units. Furthermore, data derived from this rheometry technique provides better understanding of the parameters useful in predicting extrudability. Finally, there was found to be an interesting byproduct of this viscometry concept, namely, the characterization of external and internal lubricants from the standpoints of viscosity reduction and frictional heat generation. Further, the researcher found on a theoretical level that the area under the torque curve from the Brabender Plastic-Corder recorder had wide application in that various critically important rheometric developments could be monitored. The rheometric data thus produced was comparable to those employing more formal techniques and that the torque rheometry was pragmatically sound. Since that time, further application data for integrated torque curves has developed. While mechanical and electronic planimetry devices currently on the market were examined for this application, none exhibited the sensitivity required. Thus, there arose a need for a versatile integration system to meet the needs of present-day plastics technology through measurement of torque and subsequent integration of torque curves.